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PCA9517: No SDA signal in B side

Lacey Lin
Intellectual 2900 points
Part Number: PCA9517


Hi team,

My customer use the PCA9517 as below:

But there is no SDA signal in SDAB side, the test results are as blow. The SCLK are all OK in A side and B side.

Yellow is the SDAA, green is SDAB

The yellow is SCLKA, green is the SCLKB.

Can you help to review the schematic and comments what may be the cause for this?

Lacey

Thanks a lot!

  • 0
    TI__Prodigy 280 points

    Hi Lacey,

    Can you please ask the customer for more images of the surrounding circuitry? For example, I do not see pullup resistors on the B side of the device. Based on the SCLK signals it appears as though they exists, but on the SDA image the B side does not appear to be high in steady state. Note that when undriven, the lines should be pulled up to their respective VCC. 

  • 0 in reply to Paul Gomez - TRX
    TI__Intellectual 2900 points
    Hi Paul,
    The pull up resistor in B side is 2K.
    So now it seems the B side has went into a stuck state and the voltage is keeping as 0.7V all the time.
    Reset or power cycle will not cover the failure state.
    And only this device can reproduce this failure.
    Can you help to analyze what may be the cause? Is there some circuit damage that can cause this failure?
    Lacey
    Thanks a lot!
  • 0 in reply to Lacey Lin
    TI__Intellectual 2900 points

    Hi Paul,

    My customer have replaced the PCA9517 with a PCA9617, the issue is still. So it seems it’s not a single chip failure issue.

    They have also changed the R28 to 0 ohm and removed the R28, the SDAB still don’t have signal and it’s in low level all the time.

    Please help to double check the schematic and the issue wave.

    Can you help to comment what may be the cause? They have checked the other circuit and can’t find any suspect cause.

     

    Lacey

    Thanks a lot!

  • 0 in reply to Lacey Lin
    TI__Prodigy 280 points

    Hi Lacey,

    Allow me to make the following requests:

    1) Can you please request a physical picture from the customer so we can verify the top symbol on the package?
    2) Please ask the customer to disable, or even unpopulate, the device and check again with the scope to verify the SDAB behavior persist.

  • 0 in reply to Paul Gomez - TRX
    TI__Intellectual 2900 points
    Hi Paul
    1. The customer can just provide the silkscreen, and it's
    TI 79
    AYK
    2. you mean if we remove the device or not power on the device and check the signal of the SDAB?

    Lacey
    Thanks a lot!
  • 0 in reply to Lacey Lin
    TI__Prodigy 280 points

    Hi Lacey,

    For item #2, you should be able to probe the line on SDAB with the device disabled (EN low) or completely removed. Since the line is weakly pulled up, you should measure a high. If not, the leakage path must be somewhere else on the node. If the line goes high, then it may be our device causing this behavior. 

  • 0 in reply to Paul Gomez - TRX
    TI__Guru 62920 points
    Hi Lacey,

    I just wanted to check back in - do you have any updates regarding this issue?

    Thanks,
    Max